Shift control apparatus for automatic transmission

Abstract

A shift controller controls a downshift to a low shift speed, spaced apart from a high shift speed by two or more steps, through an intermediate shift speed, by first releasing first and second shift release elements, then engaging a first shift engagement element, and finally engaging a second shift engagement element, while controlling the torque capacity of the second shift release element by feedback control. As a result of releasing the first and second shift release elements before engaging the first shift engagement element, it is possible to rev up an input rotation at maximum performance of an engine to reduce the time for shifting. As a result of the feedback control of the torque capacity of the second shift release element after engaging the first shift engagement element, a torque fluctuation at the intermediate shift speed can be reduced to avoid occurrence of an uncomfortable shift shock.

1. A shift control apparatus for an automatic transmission, the shift control apparatus comprising:
 a controller configured to control the automatic transmission;
 wherein the automatic transmission comprises a plurality of friction engagement elements whose engagement states achieve a plurality of corresponding power transmission paths in a speed change gear mechanism; and 
 wherein the automatic transmission is configured to shift speeds by switching engagement among the plurality of friction engagement elements; 
 
 wherein the controller is configured to control a downshift from a higher shift speed to a lower shift speed, through an intermediate shift speed, by disconnecting and connecting respective pairs of the plurality of friction engagement elements at a single switching of the engagement; 
 wherein the lower shift speed is spaced apart from the higher shift speed by two or more steps; 
 wherein the pairs of the plurality of friction engagement elements comprise:
 a first pair comprising:
 a first shift release element that is in an engaged state at the higher shift speed and that is released during shifting from the higher shift speed to the intermediate shift speed; and 
 a second shift release element that is in an engaged state at both the higher shift speed and the intermediate shift speed and that is released during shifting from the intermediate shift speed to the lower shift speed; and 
 
 a second pair comprising:
 a first shift engagement element that is in a released state at the higher shift speed and that is engaged at the intermediate shift speed and maintains engagement until reaching the lower shift speed; and 
 a second shift engagement element that is in a released state at both the higher shift speed and the intermediate shift speed, and that is engaged at the lower shift speed; and 
 
 
 wherein the controller is configured to control the downshift to the lower shift speed by, first, completely releasing the first shift release element and releasing the second shift release element so as to make the torque capacity of the second shift release element stand by at a pressure near an engagement starting pressure, then engaging the first shift engagement element so as to acquire a predetermined torque capacity, and then engaging the second shift engagement element at a predetermined rate without a halt, while controlling the torque capacity of the second shift release element by feedback control so as to control a rotation change rate of a rotation speed of the automatic transmission to become a target rotational acceleration.